Homing pigeons are well known for their
extraordinary sense of direction, but how exactly do they navigate their way
home using the Earth’s magnetic field?
Homing
pigeons are well known for their extraordinary sense of direction, but how
exactly do they navigate their way home using the Earth’s magnetic field?
Most
researchers believe that the homing ability of pigeons is based on the “compass
and map” model, in which the birds rely on the sun like a “compass” and the
Earth’s magnetic fields as the “map” to navigate back to their nests.
In
pigeons, this magnetic field “map” was believed to be read with the help of a
certain type of white blood cells called macrophages.
New
research published in Nature has debunked this established dogma, revealing
that the macrophages thought to be the center of the magnetic sense in birds
are in fact not responsive to magnetic fields.
In this
study, a collaborative effort between the University of Western Australia (UWA)
and the Institute of Molecular Pathology in Vienna, the team characterized the
iron-rich cells in the upper beak of pigeons using a technique called
transmission electron microscopy (TEM), which passes a beam of high-energy
electrons through tissue samples.
The
team analyzed the distribution and type of iron minerals in pigeon tissues and
discovered that they were not magnetosensitive neurons as originally thought.
“It
took a team of Australians and Austrians to show that the established dogma in
the field was completely wrong. The mystery of how animals detect magnetic
fields has just got more mysterious,” said Dr. David Keays, who works at the
Institute of Molecular Pathology in Vienna.
Apart
from the beak, these iron-rich macrophage cells were also widely found in other
parts of the body, including the feather follicle and skin cells.
“Our
contribution confirmed that the iron in the macrophage cells in the pigeon beak
were normal iron deposits composed primarily of protein bound iron in the form
of ferrihydrite, similar to that found in many other animals. Magnetite is
thought to be the likely candidate magnetic material,” said Dr. Jeremy Shaw
from the UWA.
Their
unexpected finding has reset the current dogma in avian navigation and brings
scientists back to square one – finding the true location of the magnetic sense
in homing pigeons, as well as other migratory species including bees, rainbow
trout, and sea turtles.
The
article can be found at: Trieber CD et al. (2012)
Clusters of iron-rich cells in the upper beak of pigeons are macrophages not
magnetosensitive neurons.
AsianScientist
Source: University of Western Australia
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